Highly pathogenic emerging viruses are a major concern for global public health as highlighted by the current Ebola virus outbreak in West Africa. Different members of the ebolavirus family demonstrate significant differences in pathogenicity in humans ranging from case fatality rates of 40-90% for Ebola virus (EBOV) to asymptomatic infections with Reston virus (RESTV). Determining the factors that lead to the attenuated phenotype of RESTV in humans is hampered by the lack of infection models that recapitulate the observed differences of RESTV and EBOV infection in humans. In Aim 1 of this application, we propose to establish a novel model system based on human primary cells to dissect the host responses to EBOV and RESTV infection and identify possible correlates of protection. Using human induced pluripotent stem cells (iPSCs), we will generate two target cell types of EBOV infection which are thought to play a major role in EBOV pathogenicity, myeloid dendritic cells (mDCs) and primary hepatocytes. While there is evidence that EBOV infection impairs or dysregulates the antiviral response in myeloid cells (see significance and preliminary data), hepatocytes are thought to be involved in the massive, uncontrolled virus production observed in EBOV infection. We will use the iPSC-based platforms to define the differences in the host response to high and low pathogenic ebolaviruses in order to identify possible correlates of protection. In Aim 2, we propose to establish a replicon-VLP (viral like particle) system for EBOV and RESTV which can be used in primary cells to dissect the different steps in the virus life cycle and connect them to observed differences in the host response to infection. A better understanding of ebolavirus pathogenesis by examination of differences between high and low pathogenic members in primary cells will provide much needed insights in determinants of pathogenicity in humans and will inform more targeted approaches for the future development of therapeutics.